It has been known in the art for some years that triboelectric charging of the human body can degrade the appearance of footwear and clothing. Static electricity can cause shoes to attract dust, making them look dirty and used. It can also cause sheer garments to cling and clump to the wearer's body, and may cause one's hair to cling and become unruly, especially if one's hair is fine and long. In the fashion world, a great deal of attention and money is spent on the electrostatic problems of clinging clothing and unruly hair. Recent articles that described tactics and products for mitigating “static hair” appeared in New York Magazine, The Huffington Post, and Good Housekeeping, to name just a few.
Furthermore, triboelectric body charging can cause a great deal of discomfort. Many people experience painful and disturbing electrical shocks due to electrostatic discharge (ESD) after walking on carpeting or vinyl flooring.
Even more prevalent and disturbing are shocks and sparks that occur when people exit their vehicles during dry weather. Furthermore, reports by the Petroleum Equipment Institute in 2010 (Renkes, 2010, cited below) suggest that such sparks were likely the cause of almost two hundred fires, some deadly, that occurred when consumers pumped gasoline at filling stations in the U.S., from 1999 to 2004. Numerous other petroleum industry studies (for example, American Petroleum Institute, 2014, cited below) provide evidence of human body charging as the cause of fires. Dozens of patents and patent applications that attempt to address this problem—some recently assigned to major companies, such as General Motors, Honda, and Volkswagen—have been filed and issued in attempts to address these problems, with results that are unsatisfactory due to cost, complexity, unreliability, and ineffectiveness.
Human body triboelectric charging has also been implicated in the unintentional deployment of some vehicle air bags (Hearn, 2014, cited below). Detrimental effects of ESD on pacemaker operation have even been reported (Barold, 2001, cited below).
Most consumer ESD problems are caused by the triboelectric human body charging that occurs when a person's apparel separates from dissimilar materials. This can happen when the person's clothing separates from seating surfaces, or when his or her footwear separates from vinyl flooring while walking, for example. After a person has been charged, the behavior and appearance of clothing and hair may first be adversely affected, as mentioned above. Then, he or she may touch a grounded, uncharged or oppositely charged object, such as a vehicle or an appliance, and be discharged in a painful manner.
To study the ESD problem, the electrostatic voltages of test subjects and other objects were measured with an ACL Model 300B electrostatic field locator. Because it is well-known that the level of humidity of the air often affects electrostatic processes, a UEI Model DTH31 Digital Psychrometer was used to monitor ambient air temperature, relative humidity, and dew point temperature during testing. Internet weather service reports of these same ambient air parameters were also noted during tests.
Initial testing verified that the disturbing ESD that many people experience when exiting their vehicles, for example, is typically caused by human body charging, not vehicle charging. Test vehicle voltages were always found to be essentially zero, regardless of the season or weather conditions; this is thought to be due to the prevalence of mild electrical conductance in modern tires. In contrast, the body voltages of test subjects were found to be quite high at times. It was further observed that the incidence and severity of vehicle-related ESD events seemed to be worse in the autumn than in the winter. Given that lower humidity generally exacerbates ESD problems, this observation initially seemed to contradict the fact that air humidity is typically even lower in the winter than in autumn. However, further testing and observations revealed that, in the winter, subjects' footwear was more likely to be contaminated by substances such as salt, melted snow, and mud. The contaminated footwear had a relatively higher electrical conductance, which effectively connected the subjects to ground, thereby mitigating ESD effects in the winter.
These observations suggested that the use of static dissipative (SD) shoes would be effective for mitigating the problems mentioned above.
Conventional SD shoes have a well-defined conductance that is appropriate for mitigating ESD related to body charging. They have been commercially available for decades, but, until now, their marketing has been focused on niche markets, such as towards workers in the electronics assembly, flammable chemical, and fuels industries. The characteristics of certified SD-rated footwear can be found in ASTM F2413, “Standard Specification for Performance Requirements for Foot Protection” (cited below).
The benefits that would accrue from the wearing of SD shoes by the general public would be significant in the areas of consumer appearance, personal comfort, and safety. Unfortunately, the vast majority of existing shoes have no SD qualities, and the relatively limited number of existing shoes that do have SD ratings have serious disadvantages. Since significant human body charging occurs many hundreds of millions of times per year or more in the U.S. alone, an innovation that will expand the use of SD shoes by the general public is needed.